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[koonal.basu@ril.com]

In our Sour Water Strippers, we have a single Horizontal Circulating Thermosiphon Reboiler attached to each stripper. In phenolic service these reboilers get fouled frequently resulting in very low runlength of the strippers. Fouling material is mainly corrosion products and carbon. I have a few queries on this matter which I have mentioned below.
 
1) Is the Filter / Coalescer unit at stripper feed effective and being operated successfully anywhere in the world?
2) What kind of Reboiler design is best for such a fouling service. Is forced circulation a better design? Can the existing horizontal circulating thermosiphon be changed to forced circulation with a filter/strainer at pump discharge? 
3) Is a chemical treatment system effective in terms of separation of fouling materials and in terms of opex as well. Please share any such chemical treatment system which is successfully being operated at a similar service. 
4) We are already working on preventing the foulants at the source itself. But if there is any best design and operating information available which can be implemented at SWSU itself, please share. 
 
System Description:
We process about 180 m3/h phenolic sour water at each of the two parallel stripping units. This water comes from DCU and FCCU. It has 0.4wt% NH3 & H2S and stripped to 30 ppm NH3 and 10 ppm H2S. We inject 6.6%caustic and maintain pH=9 at stripped water. Sour water is first degassed at 2.0 kg/cm2g pressure and then goes to a Feed Preparation Tank having almost 20 Hrs residence time and 20mBarg pressure.There are 3 exchangers in series as stripper feed/bottom exchanger. The Reboiler heating medium is LP steam (4 barg pressure) which is controlled at the Condensate line with a flow control valve. To maintain Stripper top temp, we have pump around system which draws water from the 6th tray(from top), cools it down and returns it back at the top tray.